Most building control systems or building automation systems operate to provide ventilation in the spaces of a building. Ventilation is important because living occupants within a building utilize the available oxygen in the ambient air over time through respiration. In addition, work equipment and/or work materials can add irritating or harmful chemicals to the air being respirated by the occupants.
For many years, heating, ventilation and air conditioning (“HVAC”) systems have provided a mixture of fresh air into the chilled or heated supply air for the building. This supply air flows into the spaces and rooms of a building through ventilation dampers, as is well known. HVAC systems can increase or decrease the mixture of fresh air into the supply air based on control variables. Currently, the mixture of fresh air is controlled based on measurements taken in the return air of a building system. If the return air is relatively low in oxygen content (or high in CO2 or CO content), then the mixture of fresh air may be increased. If the oxygen content is adequate, however, then the mixture of fresh air may be decreased because it is usually more efficient to perform heating and cooling on recirculated air within the building. In other control systems, the amount of fresh air is preset, and may be keyed to the time of day. For example, the amount of fresh air may be increased during work hours because more people are expected in the building.
While the existing fresh air control schemes in HVAC systems provide some rough control of the fresh air in a building, these schemes are limited. In particular, the existing systems only roughly correlate the need for fresh air with the control of fresh air. Moreover, the needs of the heating and cooling system, and efficiency thereof, may dictate the amount of fresh air that is allowed into the supply air.
Even if there were a way in which to more tightly control the amount of fresh air based on the measured need for fresh air, another drawback arises from the fact that the heated or chilled air is inseparable from the fresh air at the room level. As a consequence, a room may require more fresh air, but not more chilled air. Thus, if additional supply air is admitted to the room for the purpose of providing fresh air, then the temperature may become lower than desired. Conversely, if a particular room requires additional cooling, but does not require further ventilation, then fresh air is unnecessarily directed to spaces in which humans derive no benefit from the fresh air.
There exists a need, therefore, for a method and apparatus for ventilating fresh air into rooms or spaces of a building that addresses one or more disadvantages of the current state of the art discussed above.